Washington ? Marriage as a legal institution should be limited to “a man and a woman” and his administration is studying how best to enshrine that principle in law, President Bush said Wednesday.

Although the White House declined to say what was under consideration, Bush’s statement at a news conference raised the possibility that he might support new federal legislation — or even a constitutional amendment — to ban gay marriage.

Bush coupled his rejection of same-sex unions with a plea for tolerance, saying the United States must be a “welcoming country” that respects each individual. “I am mindful that we’re all sinners, and I caution those who may try to take the speck out of their neighbor’s eye when they got a log in their own,” he said, citing a biblical metaphor for hypocrisy.

But he said this belief “does not mean that somebody like me needs to compromise on an issue such as marriage,” which he said was “where the issue is heading” in Washington: “I believe in the sanctity of marriage. I believe a marriage is between a man and a woman. And I think we ought to codify that one way or the other. And we’ve got lawyers looking at the best way to do that.”

A White House spokeswoman, Claire Buchan, declined to say what specific proposals were under consideration or whether any had been ruled out. She said officials in the White House Counsel’s Office and Domestic Policy Council were reviewing the situation “in the context of several court cases” in New Jersey and Massachusetts seeking to legalize same-sex marriages.

In the wake of those cases, steps by Canadian courts to legalize gay unions and last month’s U.S. Supreme Court decision striking down a Texas sodomy law, congressional opponents of gay marriage have offered a constitutional amendment that would forbid it.

White House officials initially questioned whether such a move was necessary, suggesting that a 1996 federal law defining marriage as “the legal union of a man and a woman” might be sufficient. Bush’s statement Wednesday indicated some evolution in administration thinking on the question.

The issue is politically charged because conservative Christians, who strongly oppose gay marriage, form a key component of the Republican electoral coalition. In 2000 Bush sought to woo this constituency without alienating swing voters with more moderate views on social issues.

Gay-rights activists took offense at Bush’s comment that “we’re all sinners,” interpreting the remark as directed at them.

“While we respect President Bush’s religious views, it is unbecoming of the president of the United States to characterize same-sex couples as ‘sinners,”‘ said Matt Foreman, the National Gay and Lesbian Task Force’s executive director. “It’s also sad that, at a moment in history that cries out for leadership and moral courage, President Bush has instead opted for the divisive, anti-gay politics of the past.”